Fix Numeric signature coercion to properly handle null types

[Jefffrey]

Which issue does this PR close?

• N/A

Rationale for this change

For UDFs using Numeric signature with more than one argument (currently mod & pmod from datafusion-spark), they cannot handle inputs Null, Int whereas they accept Int, Null. Fixing the coercion logic to ensure both are accepted.

What changes are included in this PR?

Modify numeric type coercion handling to ignore null types

What is the testing strategy for this PR?

Added unit & SLT tests

Are there any user-facing changes?

No

[Jefffrey]

if first argument was null type, valid_type is set to it, and below when we call binary_numeric_coercion it'll fail since it expects two numeric type arguments:

datafusion/datafusion/expr-common/src/type_coercion/binary.rs

Lines 1047 to 1054 in 5b389eb

	/// Coerce `lhs_type` and `rhs_type` to a common type where both are numeric
	pub fn binary_numeric_coercion(
	lhs_type: &DataType,
	rhs_type: &DataType,
	) -> Option<DataType> {
	if !lhs_type.is_numeric() || !rhs_type.is_numeric() {
	return None;
	}

rather than fixing inside binary_numeric_coercion, decided it should be better to ensure we ignore null types initially, then run coercion on any non-null type, which is essentially what was happening in main (so long as the first type wasnt null)

[Jefffrey]

just moved this up; this would only happen if all input types were null type

[Jefffrey]

currently failing on main:

1. query failed: DataFusion error: Error during planning: For function 'mod' Null and Int64 are not coercible to a common numeric type. No function matches the given name and argument types 'mod(Null, Int64)'. You might need to add explicit type casts.
        Candidate functions:
        mod(Numeric(2))
[SQL] SELECT MOD(NULL, 3);

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.67%. Comparing base (5b389eb) to head (cd6278b).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##             main   #24988    +/-   ##
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  Coverage   81.67%   81.67%            
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  Files        1126     1126            
  Lines      414524   414782   +258     
  Branches   414524   414782   +258     
========================================
+ Hits       338558   338780   +222     
- Misses      56054    56070    +16     
- Partials    19912    19932    +20     

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